滇西腾冲地块小场钼矿化花岗岩的锆石SHRIMP U-Pb定年、地球化学及其构造意义  

Zircon SHRIMP U-Pb geochronology,geochemistry of the Xiaochang monzonitic granite with Mo mineralization and implications for tectonic setting in Tengchong Block,Western Yunnan Terrain,Southwestern China

作　　者：陈永清[1] 卢映祥 赵红娟[1] 程志中[3] 蒋成兴 刘正尚[1] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]云南省地质调查局,云南昆明650051 [3]中国地质科学院地球物理地球化学勘查研究所,河北廊坊065000

出　　处：《地学前缘》2013年第5期1-14,共14页Earth Science Frontiers

基　　金：国家自然科学基金项目(41272365;40972232;40772197)

摘　　要：腾冲地块位于东喜马拉雅东构造结的南侧翼，东以怒江-瑞丽断裂带与保山地块为邻，西以密支那缝合带与东缅地块相接。晚三叠世以来，伴随着中特提斯洋壳俯冲汇聚碰撞和新特提斯-喜马拉雅造山运动的影响，发育与板块俯冲一汇聚碰撞作用相关的花岗岩以及与花岗岩有关的锡、铅锌多金属矿化。与花岗岩有关的浸染状钼矿化是该区发现的一种新的矿化类型。通过对腾冲小场钼矿化花岗岩样品锆石U-Pb年代学、地球化学和St-Nd-Pb同位素研究，结论如下：（1）小厂钼矿化花岗岩体岩石类型为中粗粒含黑云母宽状二长花岗岩，岩体以相对富集SiO2、K2O为特征；富集K、Rb、U、Th、Pb，明显亏损Ba、Sr、P、Ti和Nb；稀土总含量（∑REE）为155．12～191．757g／g，LREE／HREE为5．67～7．78，并显示中等负Eu异常，属于富硅高钾钙碱性S型花岗岩。（2）应用SHRIMP锆石U-Pb同位素定年获得2件岩石样品的岩浆结晶年龄分别为（121．20±0．90）Ma和（121．60±0．70）Ma，戍岩年代为早白垩世晚期。应用辉钼矿Re-Os同住素定年获得3件样品戍矿模式年龄分别为（120．1±2．1）Ma、（124．5±2．6）Ma和（125．4±2．1）Ma，与成岩年龄相近，亦属于早白垩世晚期。（3）Sr-Nd—Pb同位素组成、主量元素和微量元素表明，小场合黑云母斑状二长花岗岩岩浆来自上地壳硬砂岩物质的部分熔融，依据锆浓度饱和温度计计算其熔融温度约为732-769℃。（4）在Hf-Rh-Ta和R1-R2图解上，几乎所有样品皆落入同碰撞构造环境。（5）通过上述研究推测，小场花岗岩及其钼矿化形成于早白垩世晚期怒江洋自东向西俯冲一汇聚碰撞构造旋回的陆一陆同碰撞造山环境。The Tengchong Block is tectonically located on the south side of the eastern tectonic syntaxis of Himalaya, lying to the east of East Burma Block bounded by the Myitkyina suture zone and lying to the west of Baoshan Block bounded by the Nujiang River-Ruili fault zone. Due to the subduction of Meso-Tethyan oceanic crust and the evolution of the Neo-Tethys and the Himalaya orogen, a series of granites and related tin, lead- zinc polymetallic mineralization associated with plate convergence, subduction, and collision had been developed in this block since Triassic time. The disseminated molybdenum mineralization associated with granites was discovered as a new mineralization type in this area. Based on the studies on the zircon SHRIMP U-Pb geochronology, geochemistry and Sr-Nd-Pb isotope system of the Xiaochang granite, some conclusions can be drawn as follows： （1） Xiaochang granite is medium to coarse-grained biotite-hearing monzonitic granite with porphyritic like texture, which is characteristic of high SiO2 （73. 96%-75. 70%） and K2O （4. 42%- 5.13%） contents. Total alkali （K2O＋Na2O） ranges from 5.44% to 8.03%, and the K2O/Na2O ratios vary from 1.37 to 2.00. Total content of the rare earth elements （∑REE） of the granite ranges from 155.12 to 191.75 μg/g, and LREE/HREE ratio shifts from 5.67-7.78, exhibiting medium negative Eu anomalies. On the mantle-normalized trace element distribution patterns, all the samples show pronounced negative anomalies in Ba, Sr, P, Ti and Nb but with significant positive anomalies in K, Rb, U, Th and Pb, indicating the features of silicarich high potassium calc-alkaline S-type granite. （2） The zircon SHRIMP U-Pb dating results of the two granite-samples are 121. 2O4-0. 90 Ma and 121.60-0.70 Ma, respectively, which suggests that the rock forming age of this granite belongs to the late period of the Early Cretaceous. The Re-Os dating results of three molybdenum samples from the granite are 120. 1± 2. 1 Ma, 124. 5± 2. 6 Ma and 125. 4±2. 1 Ma respectively

关 键 词：斑状二长花岗岩 锆石SHRIMP U-Pb和辉钼矿Re-Os定年 元素和Sr-Nd-Pb同位素地球化学 斑岩型Mo矿化 中特提斯同碰撞造山环境 腾冲地块 西南中国 

分 类 号：P597[天文地球—地球化学]